The invention relates to the field of optical disc signal encoding.
The invention relates to a record carrier including substantially parallel tracks exhibiting first variations of a first physical parameter of the track. The first variations represent information recorded on the record carrier. The information is recoverable by means of a controllable type of data processing. The tracks also exhibit second variations of a second physical parameter of the track. A modulation pattern of the second variations represent a code for controlling the type of data processing.
The invention further relates to a method of recording information on a record carrier. The record carrier is provided with substantially parallel tracks, and the information is encoded in first variations of a first physical parameter of the track. The information is recoverable by means of a controllable type of data processing. Also, a code for controlling the type of data processing is encoded in a modulation pattern of second variations of a second physical parameter of the track.
The invention further relates to a playback device for recovering information from the record carrier. The device includes: a reader for generating a read signal depending on the first variations, a demodulator for retrieving the code from the modulation pattern of the second variations, and a data processor for processing the read signal for recovering the information depending on the code.
A system for recording information includes a record carrier, a recording method and a playback device, is known from U.S. Pat. No. 5,724,327. The record carrier includes tracks in which the information is represented in a predefined manner by optically readable marks of first variations of a first physical parameter, such as the reflectivity of the scanned surface. The track also has second variations of a second physical parameter, such as an periodic excursion of the track in a transverse direction (further denoted as wobble), a variation in depth, shape or width of the marks. The second variations are modulated and the modulation pattern represents a code which is used for recovering the information, e.g. a de-scramble code for recovering information stored as scrambled information. The code may constitute a medium mark usable in a system for copy protection, because the track wobble cannot be copied to a recordable disc on standard recording equipment. The playback device includes a reader for reading the optical marks and a demodulator for retrieving the code from the modulation of the second variations. The player and information carrier form a system for controlled information reproduction. For this purpose, the player includes a data processor for reproducing the information depending on the retrieved code. If the information is copied on a writable information carrier, the information of this copy will not be reproduced by the player, because during the copying process, only the information represented by the first variations is written to the writable information carrier. The copied information carrier does not contain the code, as the second variations cannot be produced by standard recording devices.
Those skilled in the art are directed to U.S. Pat. Nos. 4,901,300 and 5,187,699 which describe writable CD systems. Also, world patents WO98/33176 and WO98/33325 which describes codes contained in wobble of the tracks.
The above citations are hereby incorporated herein in whole by reference.
The inventors recognized that the known system described above, cannot be applied to an existing high density record carrier like DVD, because such high density record carrier systems have tight tolerances on the parameters of the track and the required modulation of a second physical parameter would disrupt the reading of the marks and cause errors in the retrieved information.
It is an object of the invention to provide a high density record carrier with a medium mark, and recording and playback apparatus for such a record carrier.
For this purpose, the record carrier as described includes a code track that comprises the modulation pattern, the modulation pattern in the left neighboring track is aligned to the modulation pattern in the right neighboring track. The code track is a track which carries in its modulation pattern the code for controlling the data processing when retrieving the recorded information. One or more (or all) tracks on the record carrier may be code tracks. The aligned modulation patterns in the tracks neighboring the code track have the effect, that second variations in the left neighboring track are complementary to second variations in the right neighboring track, because irregularities in the second variations due to the modulation are present in both neighboring tracks. Hence, any increase in disturbance caused by a second variation in the left neighboring track is compensated by a decrease in disturbance by the complementary variation in the right neighboring track. Therefore the tight tolerances on the parameters of the track can effectively be maintained and crosstalk remains limited to acceptable values.
The invention is also based on the following recognition. The amplitude of the second variations must be sufficiently strong for detecting the modulation pattern. However, in a high density record carrier, the modulation of the second variations in neighboring tracks causes crosstalk, and therefore causes noise which degrades the detection of the recorded information and detection of the modulation pattern itself. Hence, the amplitude of the second variations must be as low as possible. The inventors have recognized that, by using aligned modulation in neighboring tracks, the maximum noise contribution of the left track does not coincide with the maximum noise contribution of the right track. Hence, a relatively low amplitude of the second variations is sufficient for reliable detection of the modulation pattern. Because of the low amplitude disruption of the reading of the marks and errors in the retrieved information are minimized.
In an embodiment of the record carrier according to the invention, the second variations are displacements of the track in a direction transverse to the longitudinal direction of the track, and displacements of the left neighboring track coincide with displacements of the right neighboring track in the same direction. This has the advantage, that the crosstalk of the first variations in an adjacent tracks is reduced, because if the excursion in the one adjacent track is towards the position of a read spot on the code track and hence causes some additional crosstalk, the excursion of the other adjacent track is away from the read spot and hence causes less crosstalk.
In an embodiment of the record carrier according to the invention, the modulation patterns in the code track and the neighboring tracks represent the same code. This has the advantage, that the detection signal of the code track will be stronger because the neighboring tracks have the same modulation. Further, if the second parameter is an excursion in a transverse direction, the distance between the tracks, also called track pitch, at the modulated parts of the track still remains the same, because both tracks have the same transverse excursion. Alternatively, the modulation pattern in the code track is substantially inverse to the modulation pattern in the left neighboring track. This has the advantage for some modulation types, e.g. a wobble in a pregroove, that the detection signal of the code track is stronger.
In an embodiment of the record carrier according to the invention, the second variations are periodic and the modulation pattern includes phase modulation, and phase differences between modulation patterns in adjacent tracks are limited to a predetermined amount. Such a predetermined amount is selected to be smaller than phase differences occurring in the phase modulation. This has the advantage, that any disturbance of the neighboring tracks is substantially in phase with a read signal from the modulation pattern in the code track.
According to the invention, a code track includes the modulation pattern, the modulation pattern in the left neighboring track is aligned to the modulation pattern in the right neighboring track. The effects and advantages of the method have been explained above with reference to the record carrier.
The playback device of the invention includes a control unit for retrieving the code from at least two tracks. In the record carrier the aligned modulation patterns result in at least two tracks having the same modulation pattern and therefore representing the same code. In the playback device, the code retrieved from a first track is verified by reading a further track, which includes the same code. This has the advantage, that the retrieval of the code is more reliable.
These and other aspects of the invention will be apparent from and elucidated further with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawings, in which